Australasian Microarray & Associated Technologies Association, AMATA

Faiz F, McNoe L, Phipps-Green M, Hollis-Moffatt J, Hook S and Merriman T
Department of Biochemistry, University of Otago, 710, Cumberland Street, Dunedin, Otago 9001, New Zealand

Type 1 diabetes is an autoimmune disease caused by impact of the environment on an individual who has inherited a complement of genetic susceptibility variants. Previously we have mapped an autoimmune diabetes locus, Idd21.1, using the non-obese diabetic (NOD) mouse model of human type 1 diabetes, to an ~15 Mb region of distal chromosome 18. This was done by congenic mapping, whereby the 15 Mb segment of DNA from a disease-resistant strain (ABH) was introgressed onto the NOD genome. The resultant congenic strain (NOD.ABH.Idd21.1) had reduced diabetes incidence. The Idd21.1 locus is of interest because it is orthologous to IDDM6, a region of human chromosome 18q12-q21 linked to type 1 diabetes. We had previously demonstrated that Idd21.1 influences autoimmune diabetes through the adaptive immune system and we had identified a phenotypic difference in activated dendritic cells between NOD and NOD.ABH.Idd21.1. The aim of the work presented here was two-fold: one, to use congenic mapping to fine-map Idd21.1 to a smaller genomic region; and two, to use microarray gene expression analysis to identify any differences in gene expression between NOD and NOD.ABH.Idd21.1 due to Idd21.1. By constructing a series of novel Idd21.1 sub-congenic strains and measuring diabetes incidence in the novel strains we mapped Idd21.1 to a <6 Mb region (76.3-82.1 Mb). Microarray experiments conducted on the NOD and NOD.ABHIdd21.1 strains showed that 103 genes were differentially expressed in activated dendritic cells. Smad2 located in the Idd21.1 region had 2-fold increased expression in NOD. These results implicate the Smad2 (Madh2) gene as containing the genetic variant underlying Idd21.1 in murine autoimmune diabetes. Smad2 competes with Smad3 for binding to Smad4, thus inhibiting expression of Smad3-dependent genes involved in apoptosis.